One of the process steps employed in petroleum refining is the separation of olefins from paraffin-rich streams. Low-temperature distillation is commonly used for this purpose. See, for example, Bryan, P. F., “Removal of propylene from fuel-grade propane. Separation and Purification Reviews, 33, 157-182 (2004). However, distillation processes tend to be both capital and energy intensive due in large part to the low relative volatilities of the olefin and paraffin components.
Facilitated-transport membranes (e.g., immobilized liquid membranes, or ILMs) have also been used for the separation of olefins and paraffins. When used for this purpose, the ILM typically contains an olefin-transporting metal ion (e.g., Ag+) dissolved in a solvent. Such ILMs are generally selective toward olefins and have fast diffusion rates. However, they are known to suffer from a significant degree of instability due to solvent vaporization and air oxidation. Solid polymer membranes are also known for this purpose. They generally possess improved stabilities. However, a significant drawback of solid polymer membranes is their slow diffusion.
Accordingly, there is a need for liquid olefin-paraffin separation compositions which have an improved stability while possessing at least the diffusion rates and selectivities of liquid olefin-paraffin membrane compositions of the art. There is also a particular need for olefin-paraffin separation compositions having a higher silver ion content than found in conventional liquid-supported and polymer-supported membranes. The higher silver ion content would advantageously serve to increase the transport flux of olefins.